Progressive image transmission

Abstract

An image composed of binary black and white picture elements (pixels) is progressively transmitted over a narrow-band channel after binary values of all pixels have been formatted into a hierarchical structure of subdivisions of successive halvings from the entire image down to cells of pixels of uniform size and shape. Each formatted value is encoded in accordance with whether the pairs of values from which it is derived are both black, both white or mixed. Transmission of the hierarchical values involves sending the primary value representing an overall midgray mixed value, and following with successively split image values so that the entire image is reconstructed at a remote receiver in progressively finer detail down to cell size. Final resolution, when needed, results from decoding a variable length code for the permutational patterns of pixels within cells in accordance with their probabilities of occurrence. Areas once deemed monotone are complete and are subsequently skipped by both transmitter and receiver.

I claim: 
     
       1. An image transmission system (FIG. 1) including at a transmitting terminal a scanning and digitizing device (10), an addressable memory (11) for storing binary values corresponding to each picture element in an image to be transmitted and a signal processor (13) characterized in that the processor (13) at said terminal first encodes cells of binary values provided to said memory (11) by said scanning device (10) representing basic image areas of uniform size and shape according to the number of picture elements of a predetermined binary kind therein and next forms a multilevel hierarchical tree with nodal values derived from a comparison of pairs of such values on lower levels until a single value on the top level is reached according to whether the members of a pair being compared are both black, both white or mixed, each nodal value representing the shade of an equal-area subdivision for each level of said tree.   
     
     
       2. The image transmission system defined in claim 1 further characterized in that said processor (13) further encodes numerically said basic image areas of uniform size and shape according to the distribution pattern of picture elements of one kind therein.   
     
     
       3. The image transmission system according to claim 1 characterized in that processor (13) further encodes each cell of picture elements according to the permutational pattern of binary values therein and in which processor (17) reconstructs when required as a final progression the individual binary value of each picture element in the cells. 
     
     
       4. The image transmission system of claim 1 further characterized in that the receiving terminal includes a frame buffer (19) for controlling the beam characteristics of said display device (20) in accordance with the nodal values decoded by the processor (17) thereat.   
     
     
       5. The image transmission system defined in claim 1 further characterized in that said processor (13) at the transmitting terminal further encodes numerically said basic image areas of uniform size and shape according to the distribution of picture elements of one kind therein, and said processor (17) at the receiving terminal further decodes numerical values corresponding to the distribution of picture elements of one kind in basic image areas into positions of individual picture elements therein.   
     
     
       6. The image transmission system (FIG. 1) including at a receiving terminal an image display device (20) and a signal processor (17) characterized in that said processor (17) decodes nodal values of a hierarchical tree from a single apex value, corresponding to an overall image gray value, through each lower level, corresponding to successive halvings of higher image areas, and causes said display device (20) to reconstruct a transmitted image in progressively finer detail until transmission is stopped at any level or is continued to completion.   
     
     
       7. The image transmission system defined in claim 6 further characterized in that processor (17) decodes picture-element groups of uniform size and shape according to a permutational pattern of binary values in each cell and reconstructs in a final progression the individual binary value of each picture element of an original image.   
     
     
       8. An image transmission system (FIG. 1) including at a transmitting terminal a scanning device (10), an addressable memory (11) for storing black and white binary values corresponding to each picture element of an image to be transmitted, a transmission channel (15) for such image, at a receiving terminal an image display device (20) and at each of such transmitting and receiving terminals of signal processor (13,17) characterized in that a processor (13) at the transmitting terminal first encodes cells of binary values from said memory (11) representing basic image areas of uniform size and shape according to the number of picture elements therein of a predetermined binary kind and next forms a multilevel hierarchical tree with nodal values derived from a comparison of pairs of such values on lower levels until a single value on the top level is reached according to whether the members of a pair are both black, both white or mixed, each nodal value representing the shade of an equal-area subdivision for each level of such tree;   the transmitter (14) sends the nodal values level-by-level over said channel (15) beginning with said single top level value but skips any white or black value repeated to a lower level; and   the processor (17) at a receiving terminal decodes nodal values received over said channel (15) from the single topmost value, corresponding to the overall image shade, of the hierarchical tree through each lower level causing said display device (20) to reconstruct the transmitted image in progressively finer detail until transmission is stopped at any level or is continued to completion.   
     
     
       9. In an image transmission system (FIG. 1) including at a transmitting terminal a scanning device (10), an addressable memory (11) for storing black and white binary values corresponding to each picture element of an image to be transmitted, a transmission channel (15) for such image at a receiving terminal, an image display device (20), and at each of such transmitting and receiving terminals a signal processor (13,17) the method for coding and decoding picture element information for progressive transmission over such channel characterized in that in a first step processor (13) interactively with memory (11) forms picture elements into cells of uniform size and shape;   in a second step counts the number of picture elements of a predetermined binary kind in each group:   in a third step forms the base of a multilevel hierarchical tree from nodal values derived from a comparison of pairs of numbers in adjacent cells of the second step, said nodal values being both alike of one binary kind, both alike of the other binary kind, or mixed;   in a fourth step forms the remaining levels of the hierarchical tree from nodal values of lower levels according to the same code until a single value at the apex of the tree is reached, said nodal values being such that areas once determined to be all of one binary kind need not be further subdivided;   in a fifth step transmits the nodal values level by level through said transmission channel; and   in a sixth step in said processor (17) at receiving terminal interactively with said display device (20) decodes received nodal values from the apex value corresponding to the overall image shade through the nodal values of each lower level and reconstructs the transmitted image in successively finer detail until transmission is stopped at any level or continued to completion.